1. Bury it somewhere that won’t be randomly disturbed, and cannot be traced back to you (and make a map)
   1. An abandoned mine
   2. A patch of desert
   3. Inside a Glacier
   4. In an arbitrary grave
   5. In a dead body, buried in an arbitrary grave
   6. In someone’s garden, at least 6 feet down
   7. In the wall of an arbitrary root or wine cellar
   8. At the base of an old growth grape vine (since you know those aren’t going to get pulled up)
   9. Under the cobblestones of a newly paved street
   10. Given the time period, probably anywhere a little off the beaten path – 3 feet down, 6 feet away from a random road, and no-one would even know you were there.
2. Have a trusted institution guard it
   1. Deposit it in a safety deposit box at a reputable bank. Probably in Switzerland.
   2. Entrust it to a church
   3. Have it guarded as a national treasure
   4. Give it to a friend who, gives it to a friend, who gives it to another who’s been messing around.
   5. Put it in a gold bar first, to enhance the security
3. Tie it to a large piece of metal, lower it into a well on a magnent + very long string (to confirm that you can reach the bottom), pull it back up, and drop it in the well.
4. Conceal it in a piece of construction (again, map needed)
   1. Inside an arbitrary attic
   2. Or Basement
   3. Make a brick with it inside, and install that brick in a wall somewhere
   4. Climb up a church in progress, and slip it in among the stones
   5. Inside a water pipe
   6. In a fence post
   7. Inside one of 6 identical busts of Napoleon
   8. In a wall
5. Secretly Inter it with someone’s ashes in an urn
6. Cut a hole in a citrus tree, insert pen, graft on a new branch to cover the hole
7. Carve a hole in a rock, drop the pen in, place rock in an unassuming spot
8. Cover pen with something un-digestible and feed it to a long lived animal like a Tortoise
9. Slip it inside a family heirloom (not from your family)
10. Put it somewhere very public and secure, like the entry to a police station, but secured so it can’t be stolen without a lot of work (locks/boxes etc)
11. Put it inside a grandfather clock. Those don’t get disassembled, and are highly likely to remain in the same place for 50 years.
12. Glue in some out-of-the-way place in a semi-public boiler room. Somewhere that doesn’t get cleaned.
13. Stick it to the bottom of an ocean ship. It will get barnacled over before the ship comes back to port. Just keep an eye on it, and make sure you get to it before it gets scrapped
14. Create a duplicate, hide it badly, and let it be stolen. Just keep the real one in a safe at your house.
15. Keep the pen on you, and hide your own identity
    1. Go to some arbitrary colony and give them a fake name & change your appearance
    2. Live in the wilds of Canada
    3. Join the French Foreign Legion, or equivalent
    4. Murder someone and assume their identity
    5. Change your appearance in some dramatic way, like removing a leg
    6. Change your apparent gender
    7. Just go to a big city. No-one keeps track of every new resident, and there isn’t a photo of you for reference anyway.
16. Put it on something that’s always moving, like a piece of an automatic loom, so it can’t be removed
17. Give it to someone else to hide, with instructions that they should pass it on to someone you don’t know (have the map delivered back to you via delayed Western Union delivery)
18. Mail it to your fake identity in a foreign country, pick it up and re-mail it ad-infinium.
19. Carefully cut your leg open, and secrete it inside. Conceal scar with pants.
20. Glue it to the ceiling. No one ever looks up when searching.
21. In the spine of a random library book
22. Dissasemble the pen, hide the component pieces in reasonable places. Re-assemble in 50 years.
23. Replace one part of the pen with a new piece, but keep the old piece. Repeat until you have enough parts to create a second pen from the original parts. Repeat with both “original” pens. Each time one of your duplicates gets stolen, assemble a new “original” pen.
24. Don’t worry about it. There’s nothing special about Mr. Einstein or the pen. If not him with that pen, someone else or a different writing implement would be used at about that time in history to develop those theories.

Assumptions: (1) I need to do something that at least slightly decreases the chance that these "evil forces" get hold of the pen in the next 50 years, compared with some baseline that may or may not be consistent from one idea to the next. (2) I need to keep it reasonably likely that in 50 years' time I can still get hold of the pen so I can sell it to Einstein. (3) What I do needs to be at least in some sense possible in 1855, so e.g. "put it on a rocket in a highly eccentric orbit around the sun that will make it crash into the earth in 50 years' time" is no good because there are no such rockets yet. Maybe I can get fairies to hide it because fairies were "known" about in 1855, but I can't pull any time-dilation tricks using black holes because no one knew about black holes or time dilation in 1855. (4) I do actually have to be hiding the pen, in some sense; bribing the forces of evil to do a different kind of evil, or saying "screw it, there's no such thing as magic, so I don't care whether this pen is lost" won't do. (5) The forces of evil have some idea that I have the thing and what is special about it, but probably don't know too exactly what it looks like or have the ability to spy on me at all times or read my mind. -- All of this does restrict the options somewhat, so there will be some cases of Variations On A Theme below.

Remark: I'm having trouble figuring out any concrete set of assumptions about the forces of evil that doesn't rather break the puzzle. If they know who I am, they can find me and torture me or something of the sort, and although torture notoriously doesn't work very well they've got at least a good chance of figuring out where the pen is -- unless I have e.g. delegated the task of hiding it to someone else, which is a reasonable thing to do but doesn't really have 50 meaningfully different variants. And if for some reason they can't do that, then instead the problem is too easy; it doesn't seem as if I need to do anything at all. I hope the list below is at something like the intended level of paranoia.

Remark: If it means anything to say that the pen rather than Einstein is magical, perhaps I should forget about hiding it and start using it to write physics papers myself, and see what happens. (Hmm... Am I by any chance James Clerk Maxwell? The timing kinda checks out.)

1. Put it in a nondescript box somewhere.
2. Disguise it as something else. A magic wand, a stick, etc.
3. Build it into an item of furniture: the leg of a table, perhaps.
4. Bury it.
5. Just use it as a pen. The forces of evil will never expect that something I'm treating so mundane a way could be so magical.
6. Disguise it as, or hide it inside, something else, and then give that to someone else to hide, giving them an entirely false story about what it is and why it needs to be hidden.
7. Make a replica having (so far as I know) no magical powers whatever, and conspicuously hide the replica in some manner that the forces of evil can defeat but not without substantial effort. Hope that they do so and then think they've won. If so, it doesn't much matter what I do with the real magic pen.
8. Make many, many replicas. In this case I'm not trying to fool the forces of evil, merely to DDOS them. Of course I will need some way to identify the real one; maybe I give them all serial numbers and I remember which number goes with the magic pen.
9. Make many replicas. Make no attempt to know which is the right one (so e.g. the forces of evil can't discover which is which by torturing me). Then, fifty years from now, sell them all to Einstein. According to the problem specification, the inexorable Laws of Magic then guarantee that, since I've sold him the magic pen, he will use that one to write his papers.
10. Do nothing. Apparently some infallible magical oracle has told me that I will sell Einstein this pen in 50 years and he'll use it to write papers about his relatives, or something. If so, the forces of evil can't get hold of it in any way that stops that happening.
11. Use whatever powers of clairvoyance enabled me to know that I'll sell the pen to Einstein, etc., to determine where the forces of evil will look. Put the pen somewhere else.
12. If the magic has the property that I can afford to lose part of the pen and replace it: take the pen apart and hide the parts; every now and then, collect together the hidden parts (aside from whatever bits the forces of evil have got hold of) and put them together with suitable replacement parts to make a whole pen, so I again have a single magic pen; then repeat. This way the forces of evil need to steal more than one pen's worth of parts in order to win.
13. Make sure that wherever I go, I carry a strong metal box, about 20cm long and 5cm across, and that I frequently check that it hasn't been lost. The forces of evil will assume that this contains the pen. Eventually they will no doubt steal it from me. Of course the pen is actually somewhere else entirely, and the forces of evil have wasted a lot of time and effort. (This needs to be combined with other techniques.)
14. Deposit it discreetly with a Swiss bank. This will both keep the pen safe and have it conveniently positioned for sale to Einstein in Zurich.
15. Sew it into the hem (or some similar bit) of an article of clothing I wear. Transfer it from one to another often enough that I don't arouse suspicion by wearing the same thing all the time. This way the pen is always on my person and hence harder to steal.
16. Shove it in a desk drawer along with all my other pens, making no effort to remember which one it is. As with #5 above, this should avoid suspicion. As with #9 above, sell the entire contents of the drawer to Einstein in 50 years' time.
17. Place it in a hollowed-out book, among thousands on my shelves. (I do in fact have thousands of books. That was probably much harder in 1855 than it is now, so maybe it's only hundreds; that could still be sufficient.)
18. I think 1855 is late enough that I might plausibly have plumbing in my house of roughly the kind we have today. Fit some extra pipes, made to look as if they carry water or, better, sewage, but in fact don't, and hide the pen inside one of those.
19. Hide it within a wall of my house. It had better be one I was intending to repaint anyway, to hide the newly replaced mortar or drilled-out brick or whatever.
20. Acquire the habit of collecting musical instruments. Place the pen inside the tubing of a brass or woodwind instrument that I don't know how to play.
21. Become a keen hunter. Place the pen inside one barrel of a double-barrelled shotgun. (Because then, with a bit of care, perhaps I can still shoot with it, making it less prominent as That Gun I Never Actually Use.)
22. If I have a few years before the forces of evil catch up with me: drill out a bit of a growing tree trunk and put the pen in there; the tree will continue growing and engulf it, hopefully in a way that doesn't make the history too obvious.
23. Persuade a surgeon to embed it in one of my thighbones. (I don't know whether this is actually possible. It again depends on not being observed by the forces of evil until I've had time to recover from this rather drastic procedure.)
24. Persuade a builder to incorporate it into a house newly built.
25. Obviously the magic bit must be the nib, right? That's the only part that does the actual writing. Well, it seems like we could incorporate a pen nib easily enough into the insides of an old-style pocketwatch. Watch-making is therefore my new profession; build the nib somehow into the workings of a particularly elegant watch and sell it to someone I can rely upon to keep it for display rather than using it or selling it on. Fifty years later, buy it back. (Einstein, on discovering this way of securing magical physics-paper-writing pens: "If I had known, I would have become a watchmaker.")
26. It seems that in many of these schemes the weakest link is me. So let's hide me and hopefully the pen with me. Fake suicide or accidental death and start a new life with a new name, taking nothing but the clothes I'm wearing ... and this pen I happen to be carrying.
27. Travel abroad, moving on from each location to another as quickly as possible. Back in 1855 I don't think it was so easy to follow someone through a lengthy sequence of such moves. Change name from time to time if possible. End up somewhere out of the way.
28. Implant it in a giant tortoise. (Might be tricky. Might be bad for the tortoise and make it not long-lived enough. Might not be possible to avoid visible marks.)
29. Apparently we are in a world with miraculous physics-inspiring pens and clairvoyance. Perhaps we have invisibility spells too: make the pen invisible.
30. Or perhaps instead there are spells of the "notice me not" type. That would do, too.
31. Or spells for teleporting objects around, in which case perhaps I can get the pen into (say) the inside of a cave a mile underground, without any risk of being seen going there. Of course this is only any use if I can get it back again later.
32. Or spells for turning things into other things, either in reality or in appearance. Perhaps instead of implanting the pen into a giant tortoise I can make it be a giant tortoise, for instance.
33. Or, combining this with the idea of hiding myself, make the start-a-new-life approach work much better by magically altering my appearance completely.
34. Or, addressing the I-am-the-weakest-link problem differently, magically suppress my memory of where I have hidden the pen for fifty years.
35. Persuade a sculptor to integrate the pen (invisibly) into a sculpture in stone, bronze or similar. This hides the pen in something solid and hard to get into, that probably isn't going anywhere in a hurry, and whose owner is likely to keep it reasonably well protected. Of course I need to be able to buy it back 50 years from now, and artwork prices are inconveniently unpredictable.
36. Hide the pen part-way up my chimney. The forces of evil are unlikely to be working as chimney-sweeps, especially as so many of those in 1855 are children, and I can just leave my chimney uncleaned or get it cleaned only by individuals I know and trust.
37. Even better than building the pen into a house, build it under a house, which had better be mine, by incorporating it into the foundations. Very difficult to steal, but of course also very difficult to retrieve; I need not to mind the expense and inconvenience of demolishing the house later.
38. Incorporate it into the frame of a bicycle. Sorry, I mean a velocipede.
39. Persuade a condemned criminal, or terminally ill patient at the point of death, to eat it. It will be buried with them, and I can dig up the body later. (Swallowing something as large as a pen is difficult, but I think there are those who can do it. And it needs to be tough enough not to be wrecked by the stomach acid.)
40. The whole scenario is absurd enough that this is plainly inside a work of fiction. So hide the pen for 50 years inside a timeskip in the work of fiction, one of those bits where years of action are replaced with (say) a row of three asterisks on a page. Maybe the next lines are "But how on earth, said George, were you able to keep it safe for all that time? -- I really don't know, replied Gareth, maybe I was just really lucky."
41. Apparently I'm some sort of merchant, since I'm going to sell this thing to Einstein in 50 years. Let's suppose I have an international trading business, much of which is made up of writing implements. Put this one in a batch of pens sent to a warehouse abroad. Make sure I move all my stock around from time to time, for camouflage. Keep it sailing around the world and take care that that batch is never actually sold.
42. I mentioned earlier that I was going to become a hunter. Ensure that some of the things I hunt, and keep the remains of around as exhibits, are birds -- pheasants, peacocks and the like. And let's say this is a quill pen. Incorporate it into the plumage of one of the birds stuffed and mounted on my wall.
43. Bribe someone at, say, the British Museum to place it inside a rarely-moved exhibit. Have them assassinated a little later just in case the forces of evil get to them. (Just as well I'm not evil, eh?) We'll need a bit more bribery in fifty years' time.
44. Earlier I proposed implanting the pen somehow into the body of a very long-lived animal. Instead, implant it somehow into the body of my beloved pet cat. It's likely that this will impair the cat's health and it will tragically die; if not, cats don't live all that long even when their health is good. When it dies I will of course be heartbroken, bury the cat somewhere, perhaps in my garden, and visit the grave regularly. And fifty years later I will dig it up and retrieve the pen.
45. Sail to a remote island (preferably one of a large archipelago for the usual "chaff" reasons), and bury the pen there. Bring no other crew, or have 'em all killed if that's impossible. (Again, it's just as well it's the other guys who are the forces of evil.) Remember, but do not write down, which island and where I buried it.
46. Simply pretend to have lost the pen. Maybe write an anguished newspaper article about how I had this extraordinary revelation about how this ordinary object might transform the world's intellectual history, and then I stupidly left it with a servant who threw it away, or something of the sort. With a bit of luck, the forces of evil will believe the story and stop searching. (The pen itself is sitting in a drawer or something.)
47. Seek out the forces of evil, and once I locate at least one of their number arrange to meet them and pretend to be naive and admiring and to think that in him or her I have found a true friend. Drop hints from time to time that I have a very important object that I need to find a safe place for. Eventually, explain that it's a pen with a mysterious destiny, that it's essential it remain safe for 50 years, that I am terrified that Someone is trying to get hold of it and disrupt that destiny, and please, you're the best and most trustworthy person I know, could I possibly impose on you by giving it to you and begging you to keep it safe for me? Oh, thank you, thank you, thank you. ... Of course what I give them is a fake. Again, the goal is to stop them bothering to search for the real pen, which is sitting in my desk.
48. Maintain a large pile of rotting manure in my garden, keeping it well supplied at all times. Good for the soil, you know. Somewhere in its depths there is a very well sealed box containing the pen. I should have enough skill with a shovel to avoid accidentally planting the pen.
49. (This one requires quite a lot of money.) Hire several teams of mercenaries to guard sealed boxes for me in various out-of-the-way places. Visit each every few months to keep up morale. One of the boxes does contain the pen. The others contain a deadly poison which will hopefully kill any of the forces of evil who are foolish enough to storm one of my outposts and retrieve the box. Given enough such outposts, it is much more likely that they give up after a couple of tragic deaths than that they find the actual pen.
50. Write down a lengthy list of increasingly ridiculous ways to try to hide such an object, and publish it somewhere where the forces of evil will easily be able to see it. Then do something else. (For obvious reasons I shall not say what.)

1. Give it to Einstein. He is a pretty smart guy
2. There were no supervillains in that time period and Einstein is causally coupled with understanding past rewrites. Causally couple the pen as soon as possible
3. Build a fort and dedicate your life on actively watching over the pen
4. Take a sinkweight and pick a sea or lake spot to place it in a low traffic and high haystack place
5. Take a lot of envelopes and have postage stamps bough for them to make a kind of chain letter where each letter intructs the receiver to drop the next letter in mail. Choose the destinatinos so that there is a lot of spatial separation over them.
6. Go into a mine, drop the pen there and blow its entrance shut and hire a mining company to excavate it in exactly 50 years. (Isn't that good for actual hiding but prevents access somewhat atleast)
7. Keep it on your person and be vigilant. You are used to watch foryour life and you have motivation not to get caught in evils jaws.
8. Just buy lots of pens. Physics ideas are not senstiive to the exact properties of pens used to write them. Just have a lot of spares that einsteins won't be out of pens even if evil tries to artificially create shortages.
9. Write the papers in advance and substitute for them if the papers fail to be made and tutor einstein on his ideas if necceary. For some reason I know about the future so proabably that is not only thing I know about the future.
10. 9 without remembering the content fo the papers use the fact that the ideas are possible or were possible in a previous timeline to tackle a challenge easier and reverse engineer equivalent contribution to nudge the state of knowledge forward approptiately.
11. Go kill the evil forces so that you know their meddling is stopped. It can't be found if nobody is looking (gold stealth ina hitman game for not having anybody alive to wittness) thinkaboutit.jpg
12. Dissamble the pen and bury them in random spots in the ground. Maybe choose spots in unlived forests?
13. I know about a future event so I have some method of accessing the future. Use the time machine to store the pen in the future so it is nowhere to be found in the past.
14. For some reason the evil forces are not targeting to kill Einstein but his pen. Place the pen in the most public place to benefit from the same restriction that prevents evil from going after Einstein (standard reason would be soe sort of masquarade but who knows)
15. Place it in the safe of the most prestegious bank.
16. Pen is a pretty light object. Try to design a rocket that will store it in orbit to hide it in the vastness of space. People in modern times can get cameras into suborbital paths for cool photos. Good luck designing a retreival vechicle or you need to be careful to design the orbit so that it decays in microdrag in time. (Also solve that it isn't destroyed in reentry)
17. Make some symbolic gesture or indulge time travel secrets with president so that national security level forces are used to protect the pen in presidents posession like a nuclear football.
18. You know you will sell the pen. Prove that novikov self-consistency applies to our world and have the wisdom to accept things you can not change. (requires specific state of the world)
19. Offer yourself to the evil forces as an alternative source of relativity theory so they can stop spying on einstein (requires guess on the motive to tamper with pen)
20. Scientific discoveries are often discovered independently in parrallel. It is not essential for exactly Einstein to come up with relativity. Focus on ensuring that enough scientists survive.
21. People can burn but truth never burns. Even if relativity is not discovered, it can be discovered later and is in fact available to be used. With my knowledge of the future I can bring alternatie cultural influences to offset any setback in science to make up in art to keep general progress level comparable.
22. Disassemble pen to avoid detection as the fated pen and store far away from each other to require wider intelligence operation to get sniff at them (if one parts gets tampered with is it a loss, am I actually making things harder for myself for giving more attack surface?)
23. Put in a shaystack in random farm. Introduce tradition of hiding pens in haystacks so it gets hidden ithe next haystack after the first one is cleaned up after half a year. Then just be better finder of pens with the preknowledge where the pen was initially hidden when you need to retrieve it.
24. Put it in a time capsule conveniently scheduled. Even if not physically untouchable retrieving it off-schedule would probably create unacceptable ruckus. Introduce timecapsule tradition is neccesary.
25. Flood and dominate the pen market with the exact design of the pen to have the environment too full of decoys. Yours is also probably not in anyway special so it can't even be detected to be the target outside of its causal links to come.
26. Do a private time capsule. Arson or topple down the target house when it comes time to retrieve.
27. Give the safekeeping of the pen as a mission statement of a secret organization like the free masons if not freemasons themselfs.
28. Inflitrate evil forces to know how their search is going and break out the pen from their grasp is neccesary. (cultural and special compatibility might be required)
29. Make it a cultural thing to hide pens so that there are too many people hiding pens so that the searcher gets confused on who to follow or has to spread out their investigative time.
30. Let the evil forces find a decoy pen so they get satisfied. If the pen is in no way special they might have trouble verifying they have succeeded in their mission and relax early.
31. Negotiate the hostile force away from hostile action
32. Pray (again with these non-problem specific lames)
33. Upon failure go capture hostile forces means to attack histories and make their posession of the pen target of your attack. Flip tables and copy their strategies. (conditions on failure)
34. Surgigally insert it into yourself or an ally
35. After the evils have had their way with the pen, ask it back (hope for compatible goals)
36. Make einstein try to start out with different pen and let evil succesfully grab taht one. Then prompt to make the papers proper. (Assumption about how evil targets)
37. Stage a honey pot with a trivia contest which you know that time natives do not know the answer and use it to identify or get opposition forces into trouble.
38. Destroy the pen. If I can't win they don't get to win either. (requires guess on motive. Fails mission)
39. Sell the pen early so that einstein starts to come after it, or its paper trail. He is a pretty smart guy. Might need to family heirloom or testament it to them.
40. ~60 minutes
41. Go tell Einstein of his marvelous future. now pen loss doesn't cause loss on science progress.
42. Use detailed knowledge of history to detect what is going differntly to identify where the threat is coming (assumes background knowledge I would not in fact have) ie the reading steiner approach
43. Go grab the pen from a future museum and then deliver it back after use (assumes it is a signifcant cultural artefact without the heist plot)
44. Introduce yourself as "Mr Onestone" and have the enemy steal a unrelated pen from you. Disrupt their way of identifying the target person. (assumes how evil is targeting)
45. How do I know the pen will in fact be the one that will be used? If I lose the pen I might be able to obtain one like it and hope that maybe that new one is the actual pen. Maybe I am more certain about the pen handed over to einstein being the one than I am that the one handed to me is the one. (Fights the hypothetical a little)
46. Have a causally connected thing with me from the future with me, hope that I live in a "back to the future" kind of universe and monitor my item if it it fades whether I am succeeding or not (assumes state of world, assumes posessions not speciefied)
47. Use modern material science to make a cage impervious to time native cracking methods. Time native recruitment for evil is mostly useless and modern or postmodern technology will be easier to spot.
48. Write a memoir of the worldline you are from to make the current timelines maximally technologically spoiled to offset any chronal progress lost in the shenanigans.
49. Screw this timeline. If I don't get wiped as long as I can live a prosperous life form the timeline I am from or in some future interesting magnled timeline I don't have to care about any local ruin (ie stop playing for the continuum and become a narsistist ie the cartman solution). (Fails mission)
50. Use the method used to access the past to chronoclone army to overwhelm the opposition.
51. Ask why evil does what it does and maybe get convinced or convinve them not to do it (ie Taolo The Words for the Ur-quan)

~1h 30 min

safeties

38. plans to fail: Make the pen an object of national or international pride. Make everybody attack anybody that tries to mess with it.

45. answers a different prompt: Assume a "ink is dry" universe. Ask from your departure time details about how the events nearby the writing happen. (remembering to ask before departure is good but can use some kidof temporal letter system (depends on how the future can communicate with the past, past to future letters are easy))

46. Fails to have an active component how things are better: Ask a person to hand the your pen to somebody else and make the same request making it sail from person to person whit each person makinhg independent decisions on who to hand it to. Make a termiation condition that makes it more likely to be handed back to you or just wait for it to be given back and make ti recirculate if it is too early. (hard to track but evil can also just wait for it to be handed)

49. plans to fail: Use time travel method to directly move the pen to handoff event so that vulnerability laying around the timeline is minimized

51. is a partial repeat of 31. The remaining "get convinced" factor feels separate enough to stand on its own. Additionally it can be used for moral confusion and distraction (as in Ur-quan masters the move can be used to avoid a dangerous fight)

~2 hours

This is a buffer.

This is a buffer.

This is a buffer.

This is a buffer.

This is a buffer.

1. Buy a safe, put in safe, dig deep hole, put safe in hole.

2. Keep it on your person for fifty years, and travel constantly.

3. Convince companies to mass-manufacture model of pen, and then hid it in warehouse full of same model.

4. Build time machine and entangle the pen's existence with time period of Einstein's miracle papers a la HPMOR.

5. Ship it by train, then when it arrives at a destination, have it be shipped from that place to a new, random location. Repeat.

6. Join an aboriginal tribe out-of-contact with the rest of the world and keep the pen with you until fifty years pass.

7. Time travel Albert Einstein back in time so that he writes series of miracle papers now instead of then. Create extravagant mock setup for him to live in while in the wrong time period.

8. Launch it into the stratosphere in a weather balloon that will drift around the sky for a while.

9. Have it be apparently publicly destroyed, in a way that convinces the evil forces that the pen was destroyed, when in reality, it was just a fake that was destroyed.

10. Kill the evil forces with your military might. Or maybe vigilante might.

11. Discover glitch in simulation that allows you to make infinite copies of the pen.

12. Convince government that you are from future and have them protect pen.

13. Fake the deaths of Albert Einstein's parents/grandparents.

14. Plant evidence of terrorism in evil forces so that governments attack them.

15. Hire someone to take pen from you, and then hide it for you. Then let yourself be captured with fake pen.

16. Drop pen in river and use divination to make sure that it returns to you safely.

17. Threaten family of evil forces.

18. Leave pen in your grandmother's flower vase in hospital.

19. Hide it in camouflaged tent in forest.

20. Make many large pens and place them around the world, then hide pen in random place like mountainside.

21. Send pen to space and have it hover in earth's detritus field that isn't there yet.

22. Ransom fake pen to evil forces and then it explodes, while you still have real pen.

23. Destroy all information of pen in evil force's lair, convince them that there was no pen in the first place.

24. Destroy that earth, and then travel to alternate earth where there aren't any evil forces and give pen to Einstein later.

25. Atomically disassemble pen and then reassemble when 1905.

26. Destroy pen and make albert einstein brain-model that models albert einstein having the pen in 1905. Use that instead of original.

27. Cover pen in mountain of shit, and make many mountains of shit.

28. Make the pen giant and put it on top of the whitehouse, turn it into national monument so that gov has to defend it.

29. Go back in time and kill parents of evil forces.

30. Hide pen as exhibit in museum.

31. Grow a test tube animal around the pen, and then kill animal and take pen out when 1905.

32. Convince evil forces that info is wrong, and that some other pen is the one they're looking for, and that it's a different guy who has the pen.

33. Make ai that optimizes for making pen.

34. Hide it in various dumps.

35. Smuggle into other country and start new life.

36. Send Evil forces into bankruptcy.

37. Cryogenically freeze yourself with pen under clone's supervision.

38. Make pen factory, and then become so successful with pen making that everyone has same model.

39. Tell evil forces that you destroyed pen already.

40. Hide it in nature preserve.

41. Find other important item that evil forces want to get their hands on and offer information about the guy hiding that. (Think the microphone that MLK used during his speeches, or something similar.) //really bad idea lol since it incentivizes people in similar situations to yours to rat you out

42. Turn it into an anime character, make baby anime pens with it, turn babies into pens for einstein.

43. Send it out of universe via teleportation.

44. Start a cult of worship for the pen and gather sponsers to safeguard it.

45. Give pen to Haruhi suzumiya and she will make sure nothing happens to it.

46. Provoke aliens to safeguard it.

47. Graft it to your body, and then make yourself member of evil forces group.

48. Put in giant box of steel in middle of germany and then when time comes get gov to get it out.

49. Start wars in countries where evil forces are.

50. Use pen to kill one or two of evil force's forces and use intimidation to get them to give up.

Done in 55 minutes? I had to redo one because I realized it was a copy. I also feel like I went a little too hard on the... surrealism(?) of my answers? I kind of thought to many answers of the form "Hide it in a volcano, hide it in the ocean, hide it in the marianas trench, hide it in a whale's body" seemed too same-y, but now that seems silly to me.

Ordered chronologically. In retrospect, I've assumed some pretty weak evil forces here, and mostly gone for variations on a needle-in-a-haystack type theme. 

1. Surgically implant the pen in myself
2. Theseus-duplicate the pen, give one duplicate to the evil forces so they leave me alone
3. Make a second, cooler-looking pen, ‘accidentally’ lose it to evil forces
4. Cut a hole in a dictionary/similarly boringish book, put pen in there
5. bury the pen somewhere random
6. carve a hole in a tree, put pen in, wait for tree to regrow over it
7. bury the pen, in a construction site, so it ends up underneath a building (harder to get to)
8. Hide the pen in the shaft of another, bigger pen
9. Sew the pen into the lining of a bag
10. Same but hem instead of lining
11. Make a box/piece of furniture, hide pen in the wood itself
12. Take pen apart, hide each bit somewhere different, reassemble as much as I can keep
13. Ingratiate myself with evil forces, ‘recover’ pen for them, betray them after the fifty years
14. Hand pen over to evil forces, steal back after 49 years (embed some tracking method in pen that will work in 1905)
15. Befriend a winemaker, hide pen in corked bottle of wine, keep wine for a long time ‘as an investment’
16. Hide pen in someone’s grave
17. Hide pen in someone’s grave, but by hiding it in their body and then waiting for them to die. Hope autopsies aren’t a thing yet.
18. Take pen somewhere remote, pay someone there to keep it for you
19. Keep a gun with you ‘to defend against evil forces’. Hide pen in barrel. Hope you never have to actually use the gun.
20. Convince art collectors the pen is valuable, sell to the highest bidder. Rely on whatever security they use for their collections. Fifty years later, buy the pen back.
21. Inscribe something on the inside of the barrel (so you can identify it), find as many identical pens as possible, hide them all. Good luck finding the right one in fifty years.
22. Hide at the bottom of a lake, hope lake doesn’t silt over/get dredged
23. Use the pen like you would with any other pen. Evil forces assume you’d be hiding the real pen, so that can’t be it.
24. Taxidermy
25. Become an expert in art conservation. Re-frame an old, valuable painting (hide pen in frame). Fifty years later, re-frame it again.
26. Hide pen in the walls of a new building. Demolish after fifty years.
27. Take one part off pen. Destroy the rest. Attach remaining part to a different pen after fifty years. Claim that if the ship-of-theseus thing before counted, this does too.
28. Offer pen as collateral for a huge, long-term loan.
29. Or just open a bank account and put it in your safe-deposit box, I guess.
30. Convince a member of evil forces to turn their coat. Give pen to them.
31. Hide pen in fake brick. Make building out of that plus other real bricks. Remember which brick it was, demolish building later.
32. Bury pen, plant a tree over the top (so that hopefully its root system surrounds it).
33. Give pen to nomadic group for safe-keeping, hope evil forces can’t find them.
34. Sell to pawn shop, along with as many other pens as you can get your hands on. Hope evil forces don’t know what kind of pen they’re looking for, or which of the many pawn shops you sold pens to has the right one. Inconspicuously buy back after a while.
35. Hide pen in walking stick, horribly cripple yourself, claim you just have the walking stick for the obvious reason.
36. Actually, just hide the pen in someone else’s walking stick instead.
37. Hide pen in an umbrella handle.
38. Give pen to church, claim it was, idk, used to sign Jesus’ death warrant. Have them hold on to it as a relic.
39. Remove ink from pen. Leave in the stationery cupboard at a university. Assume no-one will want it, but no-one will bother to throw it out.
40. Choose someone at random, give them the pen, tell them to keep it. Make sure evil forces don’t find out who you picked.
41. Same, but hide it under the floorboards of a random house, without its occupants knowing.
42. Using future-telling powers, give to a random future classmate of Einstein’s. Tell them to give it to Einstein when they meet him.
43. Leave pen in the stationery cupboard of the relevant patent office (again without ink if necessary).
44. Use future telling powers to work out how you’ll manage to hide the pen. Do that.
45. Decide it doesn’t matter which exact pen Einstein uses. Go into the pen-selling industry anyway. Sell him a different pen when the time comes.
46. Throw into a river, which probably then silts up and then changes course. Dig up from where the river used to be fifty years later.
47. Bury pen in an area high in some mineral people might want in fifty year’s time but don’t at the moment (silicon? uranium?). Get in to the mining industry.
48. Drop the pen in the ocean near the Netherlands. Dig up a tulip farm fifty years later.
49. Leave the pen in the dead sea for a while, until a huge salt crystal forms around it. Donate to a museum as an interesting geological specimen.
50. Bury the pen in an already-discovered archaeological site. (Become an archaeologist). Decide there was more to that area than was initially discovered, and dig it up further fifty years later.

Constraints:

• Pen needs to be secure from 1855-1905, but recovered after that

Resources:

• Depending on details, we may have some knowledge from the future

Other thoughts before diving in:

• Pen types have evolved over time - wikipedia says the ballpoint was invented around 1888
• A pen could dry out/break over 50 years; should probably keep it intact
• What type of pen did Einstein use? Apparently a fountain pen; even the exact brands/models are known (Pelikan and Waterman). Pelican didn’t produce fountain pens until 1929; Waterman was founded in 1884 and produced pens from the beginning. So, bottom line: as of 1855, we’re hiding a pen from the future. No wonder outside forces are after it; this is an extremely valuable item!

Actual answers:

1. Good luck sending a pen back in time without using relativity! If Einstein doesn’t write those papers, then the pen won’t have been here in the first place, so no need to worry about it. The pen will end up in Einstein’s hand one way or another.
2. … ok, but doing things which are naively likely to result in time paradoxes is rather suicidal, so we should probably keep that pen safe. How about just put it in a box, bury it, then dig it back up in 50 years?
3. Hide pen on a remote island which will not be visited by anyone until the early 20th century. (The British will probably have some surveying expeditions around that time, can catch a ride and pick it up.)
4. Glue some big shiny jewels to the pen and contribute it to the Crown Jewels of England. Then steal it back later.
5. … Problem is that if I can get the pen out of someplace, then so can someone else. Need to exploit some asymmetry - make it easy for me to find at the appropriate time, but hard for other people to find at other times.
6. Launch the pen into space (inside a sufficiently-durable reentry vehicle) on a trajectory which will bring it back in 50 years.
7. Issue a large bond which pays off in 50 years to the bearer of the pen. Then give the pen to a bank as collateral for a loan. The loan can be invested (using future-knowledge) to more than cover the cost of the large bond, and the bank will be incentivized to keep their pen safe. (This assumes no secondary market in bearer-pens.)
8. Leave the pen on Antarctica, then catch a ride on the Discovery expedition (1901-1904)
9. Problem reduction: after 1884, Waterman will manufacture similar pens, so we can use the leprechaun strategy.
10. Go on the offensive: leave the pen in some readily accessible place, maybe even advertise its location in the newspaper, then shoot anyone who shows up to take it.
11. Same as 10, except use a fake pen rather than risk the real one.
12. Same as 10, except don’t bother actually ambushing people who show up. Just assume that opponents will see the obvious trap as an obvious trap, and thus will not bother trying to steal the (actually real) pen.
13. Combine 10/11/12 with the leprechaun strategy: place many fake pens, all with traps, and advertise all their locations. Do the same with the real one.
14. Ok, time to play on hard mode: make it so I myself won’t know where the pen is and/or can’t access it for 50 years (so the baddies can’t just e.g. torture the information out of me). Starting point: before travelling back in time, generate a pseudorandom number from a seed known to me using a computation which I will need 50 years to replicate. Use that random number to address an envelope containing the pen plus instructions and money for the recipient, then mail it after travelling back in time, all without looking at the address. Spend the next 50 years figuring out where the pen went, then go retrieve it.
15. Attach the pen to a very durable weather balloon with a radio transmitter, then let it blow around randomly in the upper atmosphere for 30 years. Can go retrieve it after Marconi invents radio.
16. Buy a replacement pen, and swap my replacement with the pen I thought was Einstein’s before my previous self goes back in time. Then use my previous self and his look-alike pen as a decoy.
17. Seal the pen carefully, then hide it in some booze which is to be aged for 50 years. The booze’ owner will presumably keep it secure for 50 years - after all, security is probably a central concern for the sort of people who can actually manage to age booze for 50 years.
18. Throw the pen someplace where it can only be retrieved by airplane.
19. Can I make a variant of the leprechaun strategy where the relevant information is effectively time-locked for 50 years? I could number a whole bunch of pens with the true pen numbered 0, and have a few different trusted people randomly permute the pen-numbers. Those people could then each compute some function of the permutation they used, where the function is hard enough to invert that it will take me ~50 years to figure out all the permutations used.
20. Put the pen in 50 envelopes, all nested, each containing instructions to wait one year then mail the envelope to a random person. The last envelope contains instructions to mail it back to me.
21. Give the pen to some extremely paranoid and possessive person who I know will die in exactly 50 years, but give it to them on the condition that they leave it to me in their will.
22. … actually, this makes 4 more viable: attach some big shiny gems to the pen, then give it away to some individual who will die in 50 years, on the condition that they will it back to me.
23. Similar strategy: attach some big shiny gems, then loan the pen to a museum or something for 50 years.
24. Plate the pen in gold. Pick a country which had net gold inflows for roughly the 50 year period (but net outflows toward the end), and exchange the gold-plated pen for currency. Hopefully it sits in the national vault for ~50 years, and then I can trade back for it.
25. Start a betting market. Place a large bet that my pen will be stolen within the next 50 years.
26. Main bottleneck so far is that I have few ways to couple to time: technical breakthroughs/exploration, leveraging the legal/financial system, and computational barriers. What else is there? 
    1. Could always use a timer - e.g. 27, 32
    2. Astronomical events - e.g. 30, 31
    3. Other historical events - e.g. 36-38
    4. Leverage time travel some more - e.g. 33-35
27. If the evildoers want to steal the pen but not destroy it, could put it in a safe with a mechanical time-lock rigged to explode if it’s opened in the next 50 years.
28. Improvement on 19: choose a function for which serial computation of the inverse achieves large total-computational-resource savings over the best parallelizable algorithm, so opponents with large resources cannot invert it much faster than I can
29. Convince someone with lots of resources the pen is from the future and therefore very valuable. Give it to them; they’ll protect it since it’s worth a lot. After Waterman starts producing the same pen, they’ll realize it’s worthless and you can buy it back for cheap.
30. Put the pen in a buoyant container inside a nook in a rock adjacent to the ocean, so that it can only be accessed when an unusually high tide pushes up high enough, and such a high tide only occurs once every few decades.
31. Shoot the pen into a passing comet, which won’t come back for several decades.
32. Use the leprechaun trick, but write the true pen’s location/identifier on many pieces of paper, and lock them all in time-locked safes rigged to explode if tampered with. Ideally do all this without knowing the pen’s true location/identifier (similar to 19). Multiple copies ensure that the evildoers can’t just intentionally blow up one safe to destroy the information and prevent the pen from reaching Einstein - I’ll have plenty of backups.
33. Intentionally lose the pen. Then, use the time machine later to send myself a message about where it ended up.
34. Same as 33, but also encrypt the message. No sense taking chances about interception.
35. Destroy the pen, then later use the time machine again to send myself the pen from before it was destroyed.
36. Seal the pen in a (very) heat resistant container, and drop it into a volcano which will erupt in ~50 years.
37. Seal the pen in concrete in the foundation of a building which will be demolished in ~50 years.
38. Bury the pen in a time capsule which I know (from future knowledge) will not be dug up for 50 years.
39. Drop the pen in a sealed, buoyant, brightly-colored container into a crevice in a glacier which will flow into the sea in ~50 years.
40. Put the pen into a brightly-colored neutrally-buoyant vessel, and drop it into the ocean. The vessel should have a timer which, after 50 years, will drop some weights so it floats to the surface, and then make lots of noise and send out a radio signal.
41. Different subproblem: after 50 years have passed, how can I ensure that I retrieve the pen, rather than the baddies? Starting point: spend 50 years leveraging my future-knowledge to acquire lots and lots of money, then just out-resource the baddies.
42. For all of the pen-in-hard-to-access-location plans, can combine with leprechaun strategy: also hide many fake pens, so I know which one to retrieve and the baddies don’t.
43. Also, it helps if I manage to remain anonymous. In that case, I can further improve the leprechaun strategy by bringing in assistants to go retrieve some of the fake pens.
44. If I’m not anonymous, I can use look-alike assistants to retrieve fake pens.
45. Since I’m presumably spending 50 years acquiring ridiculous amounts of material wealth, I could always just pay off the baddies.
46. Rather than waiting until 1905, bring Einstein back to 1855 using the time machine. Maybe it will give him some inspiration ;)
47. I could superglue the pen to my hand, so nobody can take it, and reapply the glue regularly for 50 years.
48. … superglue wasn’t invented until 1942, so actually I’d have to make some first. On the plus side, presumably nobody will have any idea how to dissolve the stuff.
49. Hide the pen in the barrel of a historical gun in a museum which won’t be moved for ~50 years
50. Metastrategy: before actually doing any of the above, first run a mock test using a fake pen, publish the whole plan in the newspaper, and offer a reward to anyone who can break it. We call this: pen testing.

1. If there are evil forces, their are good forces; bargain with them for security.

2. Get rejected by good forces because of those paper’s role in the development of nuclear weapons; sneak it into their compound so they don’t know they are protecting it for me.

3. Prison smuggling.

4. Purchase lots of decoy pens, and put them around the world in medium security locations. Put two of them in conspicuously-higher security locations. They will never believe the second highly secure location is not the real pen.

5. The future is fixed. Do nothing unusual, because I know Einstein will get the pen anyway.

6. Infiltrate the evil forces’ security and/or archives establishment. Allow the pen to be obtained by them, and then entrusted to my care for the next 50 years. Plus, evil benefits package!

7. Throw the pen into the pile which is being sorted into boxes for sale, such that even I do not know where it winds up. Then buy all the pens of that type for sale in the shops between Einstein’s home and the patent office in 1905.

8. Get into the office supplies business, and secure the contract for supplying the patent office with pens and stationary. Even evil forces must cower in the face of bureaucracy. Engineer a retroactive sale by providing Einstein the pen, and bill him for losing it later.

9. Let evil obtain the pen, and then provide Einstein a better pen, yielding even more miraculous papers.

10. Lean on whatever mechanism granted me knowledge of the future to allow me to consistently foil the evil force’s plans.

11. Bargain with other evil forces to protect the pen, based on the argument it is necessary for the development of nuclear weapons.

12. Whine to whoever gave me the pen until they lower the requirements and I can get an A.

13. Tie the pen into a lambskin condom, and throw it on a lesser-used beach. No one examines used condoms too closely.

14. Safety deposit box. Dare they challenge the bank?

15. Hide inside a reliquary, and donate to the Vatican. Dare they challenge the Church?

16. Use the pen as collateral for a loan. If Evil obtains the pen, default on the loan on purpose, and have the repo man fetch it back.

17. Tell everyone the purpose of the pen and the situation with the evil forces. Almost no one will believe me, but it will be good enough to start a low-grade tourist attraction, allowing me to use the public eye to deter the evil forces.

18. More people will believe me than I thought. Use the credulous followers to form a militant order dedicated to the protection of the pen.

19. Put the pen in a steel container, then grow a tree around the container. For fast growing varieties, after the first few years the container will be concealed. When 1905 arrives, chop down the tree.

20. Bury the pen deeply. Much more shallowly, build a latrine on top of it. Dare they challenge the potty?

21. Skip the latrine. If I tell no one else it will be powerful difficult to find anyway.

22. Seal the pen in wax, then in a water-tight container. Bury it in diving distance off the coast.

23. Hide it in the concrete of a building being constructed, that I know will still have foundations in 1905.

24. Put the pen inside a different pen case, thus disguising it as a different kind of pen.

25. Put the pen in the mail, and ship it to a distant location. Travel to that location simultaneously, then ship it back. Repeat for 50 years. Dare they challenge the post office?

26. Put the pen inside a slightly larger pen body, thus disguising it as a different specific pen.

27. Sneak into a museum and put the pen in with some famous “Pen Used to Sign the Treaty of X” exhibit, and let the museum do the heavy lifting.

28. Create an elaborate series of treasure maps depicting the location of the pen. The maps are false, the pen is in my sock drawer.

29. Under the floorboards of my fabulous 19th century home.

30. If evil draws too close, get a 19th century home in Prague, and use the vampires to dissuade the evil forces.

31. Get to America and persuade Tesla to build an electric security system for the pen.

32. Join the military, spend the next 50 years surrounded by devoted comrades-in-arms. Carry pen in boot. Try not to accidentally win the Franco-Prussian War for France.

33. Persuade Otto von Bismarck of the importance of this pen to securing the place of the German Empire in history, and peace in future Europe.

34. Identify which part of the world is least vulnerable to the forces of evil. Immigrate there.

35. Accidentally choose the Congo Free State, realize this is evil forces headquarters. Flee north to become a hermit in the desert.

36. Become a rancher or pastoralist, and hide the pen inside several generations of livestock.

37. Become a dirigible pilot, and store the pen on an airship that spends most of its time in the sky.

38. Melt the components of the pen down into several different, small items. In 1904, commence reconstruction of these items into the original pen.

39. Pen of Theseus: replace the parts systematically over time, but never use the pen. Keep the old parts, and then build the old pen again. In this way there will be more then one genuine pen.

40. Hide the pen on the body of someone who is to be buried. Preferably not friend or family; grave robbing kith and kin is not cool.

41. Go on offense, and systematically murder every member of said evil forces.

42. In case of supernatural evil forces, learn sorcery and systematically bind or banish the evil forces.

43. Join up with whoever the evil forces arch-nemesis is. Presumably good.

44. Join up with whoever the evil forces chief rivals are. Presumably evil, and better at offense as a result.

45. #18, but dedicate the militant order to exterminating the evil forces.

46. #4 and #28 at the same time, but some maps lead to decoy pens and some lead nowhere, and some decoy pens have no map. Evil gives up in frustration.

47. Go into the pen business, and manufacture the decoys myself. Have just one prominently displayed as “Pen #1”, wail and gnash my teeth when it is stolen. The real one is still in the sock drawer.

48. Give or sell the pen to a series of other geniuses, like Kelvin, Cournot, and Gibbs. Retrieve the pen in 1905, it having absorbed their powers and put thermodynamics on a MUCH better footing early on.

49. The dead hand: put the pen in a series of explosive devices, upgrading as improvements become available (black powder -> dynamite -> munitions). I win, or everyone loses. Avoid house fires.

50. Join navy, spend next 50 years on a ship.

1. Bury it in a completely random place on the earth in a secure box, making sure I wasn't followed, record the location exactly
2. Put it in a bank vault
3. Make friends with someone who guards the crown jewels, ask them to slip it under the cushion that the crown rests on
4. Find a lot of identical pens, mix it in with them
5. Put it in my mother-in-law's kitchen drawer
6. Put it in a well-insulated box in a satellite whose orbit will decay in 50 years
7. Donate it to the Swiss patent office
8. Slip it in to the Swiss patent office (visit and put it in someone's desk)
9. Split it into pieces (cartridge, top half, bottom half etc) and attach those pieces to pieces taken from identical pens, so there are now three pens. Don't tell anyone, they hopefully won't catch on
10. weld the pen into another object
11. hide it inside a lamppost
12. Hide it inside a drainage pipe
13. Melt the constituent parts of the pen down into another form
14. Bury it in my back yard
15. Give it to Einstein's grandma
16. Give it to Einstein's school
17. Buld it into a piece of furniture (e.g. a door)
18. Hide it in a Cluedo set
19. Attach it to a flotation device and a GPS tracker and set it adrift in the middle of an ocean
20. Place it in the foundations of a building that I know will be torn down in 50 years time
21. Camouflage it
22. Feed it to a cow
23. Tie it to the top of the empire state building
24. Tie it under the golden gate bridge
25. Put it in the edge of a picture frame
26. Attach it to a magnet in CERN
27. Give it to the Royal Society, tell them what it is, ask them to hide it
28. Sink it to the bottom of the marinas trench, or somewhere less obvious
29. Give it to them - they'll be so shocked they won't believe it's the real one
30. Remove any identifying marks, and set up a company to mass-produce such pens, slip it in with the others
31. Give it to a randomly-selected person
32. Get it lost in the post
33. Put it in a high-altitude balloon with a timer set to detonate the balloon after 50 years, allowing the pen to fall to earth
34. Get it caught in a whale's balleen
35. Tie it to an Elephant's tusk
36. Hide it inside a piano
37. Hide it inside a hollow book
38. Hide it inside an oven
39. Hide it in a toilet cistern
40. Stick it underneath a fridge
41. Put it in the stuffing of a sofa
42. Hide it inside the handle of a fishing rod
43. Hide it under a railway line, inside a groove in a sleeper
44. Bury it at a (full) landfill site
45. Put it at the top of a redwood, buried in the bark
46. Hide it in a cave
47. Go to antarctica, melt a circle of ice, throw it in, so that it ends up encased in a piece of ice
48. Hide it in their own house, so they won't look for it
49. Spread as many rumours and as much misinformation about the pen as possible, to throw them off the scent, then just keep it
50. Hide it inside a really ugly pencil case

1) Dig a hole in the garden and hide it there.

2) Put it in a waterproof pouch at the bottom of the local pond

3) Put it in the same container I use to store the pens I normally use for writing

4) Put it in a pen museum

5) Hide it under the floorboards in my house

6) Put it in a safe in a bank

7) Leave it permanently in my trouser pocket

8) Have a risky surgical operation to open a cut in my body, insert the pen then seal the wound, and cut it out in 50 years time

9) Hide it in a cave

10) Go and live as a hermit in Antarctica for 50 years. Keep pen with me at all times

11) Have it stored with the crown jewels

12) Sew it into my coat

13) Put it into a puzzle box

14) Hide it at the top of a tree in a forest

15) Break into the villains den and attach it to the bottom of their leaders throne

16) Hide it under the altar in the local church

17) Hollow out a flagpole, insert pen into hole

18) Hide it under some rocks at the top of a hard to climb mountain

19) Hide it at the bottom of a barrel of beer in the cellar

20) Remove a stone from a wall, insert pen, then cover it up with a narrower stone

21) Bury it in a grave

22) Put it on a fishing boat, and sink the boat out at sea

23) Start a pen making company. Make lots of identical pens. Hide it amongst the masses.

24) Put in down the back of the sofa

25) Hide it under my bed

26) Hide it in a priest hole

27) Let the villains find a fake copy of the pen so they give up and stop looking. The real pen can then be left on display on  my mantlepiece.

28) If a small piece of a pen is removed and replaced it is still considered to be the same pen. Repeat this many times until there is nothing of the original left. As there is nothing of the original left the villains won't recognise it as the pen they are after and it can be left in plain sight.

29) Dismantle the pen into its component pieces. Put them into a container. The villains are too stupid to recognise they are the components of the pen so they can be left in the open. Reassemble the pen in fifty years.

30) Join the villains. Use position of influence within their organisation to misdirect their search in the wrong direction.

31) Spread rumours that it has been hidden somewhere else to misdirect their search.

32) Build a model of a ship. Hide pen inside the model.

33) Hide it down the spine of a book.

34) Use the pen as the pointer on a weather vane, and put it on the roof.

35) Create an early modern art style exhibition. Amongst all the junk no one will notice the pen.

36) Incorporate the pen into a wind chime in the garden.

37) Frame the villains for murder, they won't be finding the pen after they've been hanged.

38) Just make a pre-emptive strike and kill all the villains myself.

39) Add some decorations to the pen so in no longer looks like what they are expecting. They can be removed in 50 years time.

40) Give the pen to a trusted friend the villains don't know about to hide it, then go on an expedition travelling around the world to lead them on a wild goose chase.

41) Join the army, and keep the pen on me. The villains will have a hard time searching for it whilst I am surrounded by a lot of heavily armed people.

42) Join an expedition to explore the Amazon at the last moment. taking the pen with me; they will have a hard time following me.

43) Bury it in the zoo in a cage containing a lot of extremely dangerous animals. Even if they figure out where it is hidden they may be too frightened to risk going after it.

44) Bribe the local police to hide it in the police station

45) In an emergency it could be temporarily hidden up someones bottom

46) As absolute dictator of my country I will ban pens, and require that they are all handed over to me, and buried in a secure vault under my palace. Even if the villains can breach security they will have a hard time finding the one they want amongst all the confiscated pens.

47) Just hand it over to them. They refuse to believe that this is the real pen because I would never hand it over to them and throw it away so I can recover it later. As a result they look everywhere for the pen except where it actually is.

48) Let them have the pen, then  steal it back from them later, replacing it with a fake. As they believe they have the pen they won't search for it so hiding it from them is trivial.

49) Hide it inside a grandfather clock

50) When they come to interrogate me try and engage them in a long conversation, preferably one which involves them boasting about their future plans; whilst my friend goes out the back door to take the pen to a safer location.

Dig a hole and bury it

Disassemble it and give each piece to a trusted family

Place it into a lockbox at a reputable bank

Store it in a drawer and include detailed instructions in my will

Find Einstein's parents and give them the pen

Place it in a drawer with a sealed letter describing what should be done if found

Put it in a tree's branches

Carve a hole in a tree trunk and place it in the hole

Seal it in a chest and drop it in a lake with an anchor

Glue it to one of those tortoises that lives a long time

Photograph or draw it, make a replica in 50 years

Keep it in an important document like my passport, moving it each time I renew

Convince the Pope the pen is holy and must be preserved

Convince a museum the pen is fine art and should be displayed

Carry it everywhere I go

Give it to a stranger with a promise to pay them if they return it in a year. Repeat 50 times

Become a head of state and pass a law to protect the pen

Start a pen manufacturing company and produce millions of copies of the pen

Start a pen-worshipping cult

Negotiate with the evil forces to return the pen to me later

Convince the evil forces to give the pen to Einstein

Place it in a sewer

Start a family and teach my kids to protect the pen

Join the evil forces, work my way to power, and change the organization's objective

Infiltrate the evil forces and assassinate their leadership

Give the evil forces a counterfeit pen

Change my name so the evil forces can't find me

Become a hermit living in a cave

Learn self-defense to protect the pen if attacked by evil forces

Hand the evil forces the pen and then take it back, as they "obtained" it

Give the evil forces the part of the pen they want and replace it

Invent time travel and send the pen to the future

Invent space travel and send the pen to space

Place the pen in a body to be buried

Place the pen in the foundation of a new building

Shoot the pen high into the atmosphere so that it circles the earth for 50 years before landing

Place at the bottom of a jar of pennies

Place at the bottom of a chewing tobacco spittoon

Disguise as a record player's needle

Just keep it on my desk amongst my regular pens

Hide it in a residential attic

Hide it in a mattress

Hire a private security team to guard the pen

Protect the pen in a secure facility with booby traps

Convince the evil forces they don't really want the pen

Hide the pen in the handle of a sword

Ass pen (https://www.youtube.com/watch?v=w12RKy966OU)

Start a foundation and place the pen in trust

Tag someone else "it", now they have to hide the pen

Forget about the pen, Einstein will probably write his papers anyway

So, my first "actual" comment:

1. Implant the pen into my body.
2. Hide it in an umbrella, but also integrate a weapon (Mycroft Holmes Style) to have good non-pen reason to carry it allround all the time.
3. Every few months change one's identity and the hiding spot.
4. Struggle to keep it hidden till Einstein is of age to think about a good solution. Ask him inderectly.
5. Charm the pen with partial transfiguration since it is known for being not possible. Therefore it cannot be the pen.
6. Make it look like something else: stick, wand etc.
7. Weren't there somebody who could swallow various items and get them easily back out? Learn that skill to hide the pen.
8. Contact a ravenclaw, ask for help, in exchange they will be able to read the miracle papers.
9. Build a time machine or accidently find one which somebody lost, notice confusion & be curious, push a few buttons, land in 2020, survive, find out about computers, the internet and LessWrong. Ask the community indirectly about hiding ideas for Einstein's pen (for example you could create bubble challenges)
10. The Effective Altruism Community might also be a ... äh... "Anlaufstelle".
11. With the help of an magic hat turn the pen into a white rabbit, change it back and forth now and then to prevent it from dying,
12. Buy lots and lots of pens, keep the original and drop/trade/gift /whatever them (afterwards you have to clean up of course).
13. Glue a flower on it and wear a bun with your self made hairstick.
14. Make a fire and "burn" the pen (the thing where the fire is on top should have a hole somewhere, where it can be dropped in), while laughing evilly. Use the moment of confusion and make a run for it. Carry on for fifty years.
15. Put it in the ground and let plants grow over it.
16. Sew secret pockets in your clothes.
17. If it is likely that the evil forces find and torture you one day: Give your best friend a letter which she will return in fifty years, which asks you to find something and sell it to someone. In exchange you will get reward. Hide the pen and than get wasted. Live peacefully as much as possible.
18. Put it in a safe.
19. Put it in a hollowed-out book and hide it in your library -> evil forces are not truth seeking fellows.
20. Hide it in a grave.
21. Let it be blessed by a priest or something.
22. Pour it in resin. For example as a table top.
23. Do not do anything, let time travelers solve the problem which lead to their future misery/slow progress.
24. Everytime the evil forces come too close, I just sing to keep them away.
25. Try to sell it to the evil forces but change the conditions last minute everytime or make the conditions not obviously impossible, so that they try fifty years to meet them.
26. Hide it in your diary.
27. Hide it under you pillow.
28. okay this one is weird... (I forgot what was weird so here is another one): Have a house, remove loose brick, insert pen, insert brick.
29. Hide it on the doorframe or under the door rug (works always).
30. Put it in an handbag of an old woman (if you feel bad for the old woman: be the old woman)
31. Make the best of the situation and decide to finally go see the world (constantly move around)
32. Marry a rich and important person, use them to your advantage.
33. Hide it in those big gowns, your own or seduce somebody.
34. If the pen is not really big you can hide it in those special belts.
35. Use it as the starter for a bomb (if it gets removed, the bomb explodes(under the condition that the evil forces are not immun and not suicidal)), expiry date in fifty years.
36. Send it around, but make the evil forces believe that you still have it on yourself.
37. Put it in the ground, where a house is supposed to be build.
38. Wear it as a necklace hidden under your clothes.
39. Get a witch to help you. Might be interested in miracle papers.
40. Learn how to hold great speeches. Manipulate other people so they fight and distract the evil forces.
41. My dog can teleport himself. He should be easily able to fend evil forces for fifty years off.
42. Wear boots, put pen inside.
43. Hide it in a picture frame.
44. Hide it in the thing a horse wears, train it so that it kicks everything and anyone who is not you.
45. Get Sherlock to help you.
46. Hide it inside the bible or crucifix.
47. Get people to worship and defend the pen at all costs in combination with a prophecy about you getting it back in fifty years.
48. Hide it in a secret space in the floor.
49. Put a note on it "Not of interest in any way" or charm it in a way that evil forces cannot perceive it in any way.
50. Put it like a candle in a chandelier.

I hope this is okay :)

Edit: Here's some buffer text, because the sidebar shows things even inside spoilers. Buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, buffer text, and more buffer text.

1. Keep it in your pocket
2. Hide it inside a chair leg
3. Bury in it your garden
4. Attach a weight to it and throw it over a pier into the ocean (use a fishing magnet to retrieve)
5. Surgically implant it in yourself
6. Surgically implant it in a volunteer
7. Use your bank's safe deposit box
8. Pay someone else to hide it for you
9. Hide it inside a notable artifact that's already in a museum
10. Hide it inside a public monument, so you know that it'll be safe over the duration
11. Decoy pen
12. Make a chest of drawers with a false bottom
13. Hide it in a regular chest of drawers, underneath all the clothes
14. Place it underneath the floorboards
15. Disassemble it and reassemble its components into non-pen objects then reassemble it later
16. Dissolve it in acid (a nobel prize winner once used this to hide their medal)
17. Invent thermos flasks, and once they are popularised hide the pen in the vacuum between the exterior wall and the interior wall
18. Sneak into a construction site, and bury the pen underneath drying concrete
19. Hide it in an attic
20. Hide it in a basement
21. Hde it inside a tree
22. Bury it underneath the ballast of a railway track
23. Dissasemble it into single-material components, and then surround each component with a block of identical material. Use as paperweights
24. Hide it in between the double walls of a house
25. Invent bin liners. Hide between a bin and its bin liner
26. Cut open a teddy bear, and hide inside
27. Make a plumbing-standard pipe, with a mesh at each end. Hide pen inside pipe. Insert into your plumbing system
28. Hide it inside a hat
29. Coat in precious metals, attach a chain, wear as jewelry
30. Hide inside a fake book
31. Hide inside skirting boards
32. Hide inside a door frame
33. Hide inside a door
34. Hide inside the barrel of a gun
35. Hide inside the shaft of a spear
36. Hide inside a rail on which curtains are mounted
37. Hide on top of a tall shelf to tall for the forces of evil to reach
38. Give it to a miner to hide inside a mine
39. Hide it inside a teacher's cane
40. Hide it inside a window pane
41. Hide it on the underside of a train (if the force of evil are blindly following magic einstein-pen-trackers this should throw them for a loop)
42. Sneak it onto a ship under construction, and hide it inside the material of the ship
43. Give to someone onboard a ship you know will sink on that voyage and whose wreck will not be investigated for the relevant duration
44. Hide it inside a corpse's burial clothes
45. Hide it inside a casket/coffin/whatever-is-the-correct-name-for-the-boxes-people-are-buried-in
46. Reveal myself to a government of my choice and explain the dilemma. Leave the hiding to them
47. Throw it up into a gap inside the ornaments on the roof of a historical building
48. Hide inside a walking stick
49. Disguise as a different type of pen. Gift to political leader (so it will be both safe and well-kept)
50. Hide inside a conductor's baton

A couple of times I found myself adding an 'honourable mentions' box, and then finding a way to include it in the main list ('Gift it to someone -> that's not exactly hiding it -> disguise it first' and 'Hide it underneath a bin liner -> bin liners weren't invented yet -> invent bin liners first'). I used some somewhat absurd solutions the previous two challenges, and inspired by the more down-to-earth answers of others so I tried to limit myself to the possible (nothing outside the technology range available to me, so no inventing AIs to do the job for me) although in the spirit of babble I generally tried to make every idea somewhat workable.

Places to hide:

1. Buried (waterproof box)
2. Inside a wall cavity
3. Bank safety deposit box
4. Attic
5. Inside hollow tree
6. Get put in jail, hide pen in wall of cell. Get put back in jail 49.5 years later and recover pen
7. Give it to someone more responsible than me
8. Implant into body
9. Bluff the evil forces – just hide in plain sight, use it every day
10. Give it to the queen to store with the crown jewels
11. Turn it into an art sculpture, hide in plain sight
12. Melt down, remanufacture when required using the melted remains
13. Keep it in my pocket
14. Hide it in a sewer
15. In a crypt
16. Behind a brick in the great wall of China
17. Inside Fort Knox (or wherever gold reserves were held at the time!)
18. Underwater
19. Sole of a shoe
20. Get the president to sign something important with it, get it put in a museum under guard
21. Mould it inside a brick
22. Hide in the masonry of Pont des Invalides (or other 1855 structure of your choice)
23. Inside a statue
24. Inside hollowed out book
25. Behind false wall
26. Change appearance of pen (different colour?) as long as it is reversible
27. Inside a clock

Ways to make sure it gets to him if I die:

1. Start a conspiracy to keep it
2. Publicise to world what is happening, bring the evil forces out into the light
3. Hide it at the end of a treasure hunt with each clue more fiendish than the last. If you die, make sure Einstein gets the first clue, he can take it from there
4. Hide it in the Bern patent office in a packet with his name on it
5. Write a set of instructions on how to get the pen, give letter to Western Union to guarantee delivery at the correct time
6. Go to Colorado, hide addressed envelope with Brachiosaurus fossils and re-cover the fossils, ready for them to be dug up in 1903.

Ways to confound evil forces:

1. Learn how to lose a tail when on my way to hide the pen
2. Pretend to hide it in multiple places
3. Pretend to give it to multiple people so they don’t know who to follow
4. Go all-out attack on the evil forces
5. Put booby traps around hiding place
6. Put booby traps elsewhere to misdirect
7. Make multiple indistinguishable copies and hide all of them
8. Ensure evil forces don’t know I ever had it
9. If unsuccessful, give it to someone else, commit suicide so they can’t find out who I gave it to

Other:

1. Don’t worry about it, he can probably use whatever pen and still get the same result
2. Otherwise, use magic pen to try to write miracle papers myself
3. Buy lots of identical pens which will work just as well
4. Reverse engineer pen if no similar pens available
5. Apply magical foresight to foresee all attempts at theft and prevent them
6. Rely on determinism – apparently I already know he will write with this pen
7. Use my knowledge of modern technology to make loads of money to help with effort
8. Hide it in one of infinitely many sets each of which contains infinitely many elements, await for Ernst Zermelo to formulate his axiom of choice (1904) to allow me to arbitrarily pick it from the relevant set

• Secret pocket inside my coat.
• Convince industrialists to produce a million similar pens. Evil forces won't know the true one.
• Send a hundred accomplices to bury boxes in secret spots. One box contains the pen, only I know which.
• Just use it and leave it around as I would any normal pen. Evil forces will think it a trick, but it's actually just hiding there in plain sight.
• Disassemble pen into components, give one component to each of a set of trusted accomplices across the world.
• Launch it into orbit, inside a safe box, in such a way that it returns in about 50 years.
• 7 Find some dam or lake that predictably will run out of water in close to 50 years. Hide it at the bottom in a safe box.
• 8 Stage some hiding plot that seems kinda smart, and like I kinda tried, and get evil forces to steal pen from it, and act like "Oh no, I lost the pen, I didn't predict this, awful" -- while all along keeping a safe one in a locked safe in my room.
• 9 Devise some sort of safe algorithm where a chain of people can 1) each give the pen to each other, 2) no one knows the full extent of the chain, and 3) the chain is retraceable in 50 years for anyone who obtains some cryptographic key. Not sure how the algorithmic details would work.
• 10 Hide inside core of tree. Chop out later.
• 11 Inside block of granite in newly constructed building.
• 12 Convince evil forces that the true "pen" is actually some weird symbolic thing, like in the Da Vinci Code, and have them abandon search for true pen.
• 13 Create cult dedicated to developing extremely powerful physical and mental abilities, have them always surround and protect pen.
• 14 Inside jawbreaker that takes 50 years to get through. Also become a candy shop owner for plausible deniability about why I have that massive jawbreaker.
• 15 How much do I know about the miracle papers? If a lot, convince some other physicist I am a genius, gain their trust, and enlist their intelligence to help me think of a good hiding spot
• 16 Write the miracle papers now, but leave out one final symbol. Remove a tiny piece of the mechanism of the pen such that one can painstakingly use it to write the final symbol in 1905. Have the remaining 95% of the pen by stolen by evil forces who'll then stop looking.
• 17 Store it up your a**, like Cristopher Walken in Pulp Fiction. Sorry Einstein, it was for the greater good!
• 18 Surgical implant of pen.
• 19 Store copies of identical pens inside each book in a library. Only you know the true one.
• 20 Well, I know I will sell it to him. So I'll just give it to a random guy on the street in a foreign country; never knowing where it will end up, yet trusting that history is such that it will make its way back to me in 50 years.
• 21 Infiltrate some holy organisation, like the Vatican, and store it in a mega holy place that no one else is allowed to visit.
• 22 One of those elite Swiss safe deposit boxes.
• 23 Melt the pen. Store liquid in decorative jar. Re-mold pen when it's time.
• 24 Change my name, identity and appearance, such that evil forces don't know I am the one hiding the pen. Keep it on me at all times.
• 25 Hide it a dental prosthesis I wear
• 26 Have a long-lived bird swallow it. Become a bird watcher and friends with the bird. Take it back in 50 years.
• 27 Do lots of exposure therapy and become desensitised to scary things like snakes and spiders. Hide pen among a bunch of those scary things.
• 28 Enlist President of United States in quest -- give him pen, and ask him to keep it safe until it's time.
• 29 Inside a particular slice of train track.
• 30 Deep in mill
• 31 Deep in well
• 32 Deep inside bush of big thorns. Secretly dig tunnel underneath to get it out.
• 33 Hidden compartment in wall in London sewers.
• 34 Make pen the most treasured item of a dangerous, long-lived beast, who will protect it with its life, except from me, who tamed the beast.
• 35 Stage a fake accident where pen is destroyed.
• 36 Give it to a band of circus performers who'll pass it on down the generations -- no one can steal it from a juggler!
• 37 Make it bendable and hide it in a wrist-watch
• 38 Hide in a really difficult hall of mirrors
• 39 Steal something of value to the kidnappers, and threaten to destroy it if they make an attempt for the pen
• 40 Make the secrets of the pen a massive public sensation, and have the pen be hidden in a clearly visible public place
• 41 Offer some government/other powerful actors to run experiments on your magical premonition in exchange for keeping the pen safe
• 42 Convince evil forces that, of course, the pen is actually a piece of blackboard chalk. That's what they should be looking for. (Though, actually, it's not)
• 43 Get dreadlocks, hide it in one of them
• 44 Display it as a museum piece, while claiming that piece to be an entirely different pen
• 45 Somehow erase your memory (e.g. by hitting yourself in the head very hard), but build a system which pre-commits you to selling pens to Einstein in the future. Let history unfold.
• 46 Super heavy and hard-to-break box, with an advanced cryptographic lock that can only be opened with a secret key, where a process has been set in motion to only return the key you in 50 years. (Need to spell out what the "setting in motion" means.) If the box can be good enough, this is actually really helpful -- because changes the problem to one of hiding a piece of information for 50 years, rather than a physical pen.
• 47 Just use the part of the postal service which delivers items to yourself at a particular date in the future, of your choosing. (Sweden has this.)
• 48 Try to reason with evil forces. Maybe you can strike a bargain -- what if they get the pen in like 51 years, when Einstein is done using it for the miracle papers?
• 49 Embed it inside of your family's finest cutlery
• 50 Auction it off to the highest bidder. Who says I have to follow the plot? I can just get rich and go do other useful stuff!
• 51 Enlist the Queen of England in the plot and get her to guard it.

First get some special case for the pen so it will survive any of the scenarios.

1. Bury it very deep underground
2. Eat it
3. Get it transplanted between your organs.
4. Move to china and get a new identity
5. Put it into the sword handle of your decorational sword on your wall
6. Shoot it into orbit.
7. Get a save at a bank.
8. Build your own castle to defend the pen.
9. Paint the pen in a different color. No one will notice it is the same pen.
10. Make it invisible
11. Give it to your friend you really trust.
12. Hide the pen for 30 years and then give it to the child Albert Einstein so he can come up with his results 20 years early.
13. Send it to Albert Einsteins mother, so she can protect it.
14. Throw it into the ocean and hope the tides will bring it back 50 years later
15. Put it between your couch cushions.
16. Put it inside one of your couch cushions.
17. Lend it to a museum for 50 years and tell them about the importance of the pen. No one will expect that you put the pen on display for everyone.
18. Give the pen to Maxwell, so he can come up with relativity instead.
19. Tell your son to come up with a solution. You fear you won't be there in 50 years to protect the pen.
20. Hide it in an old tree.
21. Bring the pen to the Vatican and ask the pope to hide the pen for you in some special save?
22. Glue it to the ceiling of your appartment.
23. Hide the pen inside an art gallery with the Text: "This is not a pen" written under the display.
24. Put it into your pocket
25. Give it to a pen collector to hide it between his other pens.
26. Try really hard to remember what you learned about physics in the future and come up with the Einsteins work instead.
27. put it into a chest and tell someone that it contains something really important.
28. Send it to your parents.
29. Examine it very closely. Maybe you are able to transfer its power to other pens.
30. Become really good at making pens, so you can give Albert Einstein another pen that is just as good.
31. Hide it in a mine
32. Found a cult around the pen that will be able to protect it against those evil forces.
33. Go to iceland and hide it in the snow.
34. Go to the Sahara and hide it in the sand.
35. Hide it inside of a book you don't like.
36. get a really high tower and hide it on the roof. no one will dare to go there
37. Hide it inside of some indiana Jones Temple
38. It's 1855? Put it under your hat.
39. Hide it on a yet undiscovered Island.
40. Put it so deep under water that it can only be retrieved with technology after 1900
41. Put it into a secret pocket of your jacket.
42. Give it to powerful authorities of your country of residence
43. Give it to a construction worker to hide it in a wall.
44. Put it into the Lascaux cave. It won't be discovered for more then 80 years.
45. Close your Eyes so you can't see it.
46. throw it real high and hope it does only come back in 50 years.
47. Put it into your wallet
48. Invent the Radio and send a signal to aliens to take the pen on there spaceship.
49. Hide a fake copy of the pen in an obvious hiding place and keep the real one always with you.
50. Make 50 copies of the pen and hide all of them in seperate locations. Only you know where you hid the original one.